code: def forward_expected(self, inputs):
      y = numpy.hstack(inputs)
      return (y,)
  
file_path: chainer/tests/chainer_tests/functions_tests/array_tests/test_hstack.py
imports: import unittest
  import numpy
  import six
  from chainer import functions
  from chainer import testing
  from chainer.testing import attr
  from chainer.utils import type_check
label_desc: Use image node_id 3 for calling the TestHstack obj's underlying member method code with example usage: obj.forward_expected(inputs) and returns: y